This invention relates to a system of a combined circular/straight line light beam scan transforming apparatus and optical device and to a method for the fabrication of a circular/straight line transforming device.
Heretofore, in writing in or reading out information by means of a high-speed printer or facsimile or in detecting contaminants or flaws on the surface of a printing plate or a sheet of paper or metal, the widespread practice has been to adopt the technique of high-speed scanning by use of a light beam, particularly, a laser beam.
For the purpose of high-speed scanning with laser beams, there has been adopted a method wherein a polygonal mirror is rotated at a high speed, a laser beam is directed to the mirror in rotation, and a reflected laser beam is used as the scanning beam. Since the polygonal mirror, by the nature of its function, is required to possess extremely strict mechanical and optical precision, it has been quite expensive. Also, since the locus of a bright spot of the focussed scanning beam traces on a curved surface, it is necessary to transform this locus of bright spot to a locus on a flat surface by passing the scanning beam through a special lens (hereinafter referred to as "f..theta. lens"). This f..theta. lens has also been very expensive. In the circumstances, a method which can effect the scanning by use of light beams without resort to such expensive polygonal mirror and f..theta. lens has found popular acceptance.
To be specific, this conventional method utilizes a light-conducting element or a circular/straight line transforming device which comprises a circular/straight line transforming optical fiber assemblage having at one end thereof a cylindrical portion and at the other end a linear portion. On the cylindrical portion side, between a light-emitting element disposed on the central axis of the cylindrical portion and the contour of the cylindrical portion, there is provided a Z-shaped rotary fiber rod adapted to be freely rotated around the central axis of the cylindrical portion and composed of one end part disposed on the central axis, the other end part opposing the end surface of the cylindrical portion, and a connecting part connecting both the end parts. On the linear portion side, there is provided a photosensitive element opposing the end surface of the linear portion. The light beam issuing from the light-emitting element is admitted through one end of the Z-shaped rotary fiber in rotation and guided to the other end. The light beam which departs from the other end of the rotary fiber rod enters the cylindrical portion of the circular/straight line transforming optical fiber assemblage, propagates through this optical fiber assemblage and departs from the linear portion, thereby acting on the photosensitive element. Consequently, the circular scanning is transformed into the linear scanning. If, in this arrangement, a manuscript is substituted for the photosensitive element opposing the end surface of the linear portion and a light-receiving element is substituted for the light-emitting element on the central axis of the cylindrical portion, and the manuscript is illuminated, then the optical image of the manuscript can be transmitted to the light-receiving element along the reverse path, from the linear portion to the cylindrical portion, with the result that the linear scanning is transformed to the circular scanning.
In order for the aforementioned Z-shaped rotary fiber rod of flexible nature to be rotatably supported in position, it becomes necessary to retain the rotary fiber rod with a rigid wheel. For this purpose, the rotary fiber rod is retained with the rigid wheel in such a manner that the other end part and the connecting part of the rotary fiber rod are held in a wheel disk and the one end part of the rotary fiber rod is held in a central shaft of the wheel. The other end part of the rotary fiber, therefore, is allowed to scan the end surface of the cylindrical portion of the circular/straight line transforming device when the central shaft of the wheel journalled on a bearing is rotated with a suitable driving unit.
The diameter of the wheel, however, becomes quite large (in the order of 100 mm, for example), because the wheel by nature is required to possess a diameter equal to or greater than the diameter of the cylindrical portion. This means that the wheel inevitably possesses great mass. When the wheel of great mass is rotated at a high speed, it exerts a heavy load upon the central shaft of the wheel and the bearing supporting the shaft and does harm thereto. For this reason, in this conventional method, the rotation speed of the wheel should be limited to about 60 rotations per minute. (Refer to "Facsimile Guide '79-'80," page 62, published on May 10, 1979 by Nippon Noritsu Kyokai.)